New organic reactions of 1-alkoxyallyltriphenylphosphonium salts

Abstract

It has been found that phosphoniosilylation of $\alpha$, $\beta$ -unsaturated aldehydes with triphenylphine and trimethylsilyl triflate at -78$^\circ$C yields kinetically formed 1-silyloxyallylphosphonium salts which are cleanly rearranged to thermodynamically favored 3-silyloxyallylphosphonium salts upon warming to room temperature. Similar results are obtained with $\alpha$, $\beta$ -unsaturated acetals. $\beta$ -Functionalization of $\alpha$, $\beta$ -unsaturated aldehydes has been achieved by the reaction of 1-alkoxy-2-alkenylenephosphoranes, derived from 1-alkoxyallylphosphonium salts, with various electrophiles such as alkyl halides, acid chlorides, benzyl chloroformate, and benzenesulfenyl chloride, followed by removal of triphenylphosphine in five-step, one-pot procedure. A complete regiocontrol has been found in the reaction of 1-alkoxy-2-alkenylenephosphoranes with aldehydes. The reaction of 1-alkoxy-2-alkenylenephosphoranes with aldehydes gives $\alpha$ -adducts, whereas the reaction in the presence of trimethylsilyl triflate gives $\gamma$ -adducts. Reaction of 1-alkoxy-2-alkenylenephosphoranes with activated olefins such as vinyltriphenylphosphonium bromide, phenyl vinyl sulfone, and diphenylvinylphosphine oxide proceeds to afford functionalized cyclopropane derivatives which can be subjected to further reaction of ring expansion to give $\alpha$ -methylenecyclopentanones and substituted furans via alkoxy-accelerated rearrangement. Also, regiochemistry in reaction of direct displacement of 1-methoxy-allyltriphenylphosphonium salt with nucleophiles via easy removal of triphenylphosphine has been studied.